1. Field of the Invention
The present invention relates to a light distribution lens of a strobe device which is located in front of a light emitter and a zoom strobe device using the same.
2. Description of the Related Art
A strobe device, and particularly a strobe device incorporated in a zoom lens camera should be small and have a large guide number and a uniform emission distribution over the entire zoom range from the telephoto extremity to the wide-angle extremity (i.e., least loss of the quantity of light at the periphery of the lens), in accordance with an increase in the focal-length at the telephoto extremity. Attempts have been made to improve a light emitting tube, a reflector, and a Fresnel lens (light distribution lens). In particular, the Fresnel lens can have theoretically the same power of an equivalent convex lens, though it be made thinner in size; therefore is useful in reducing the entire thickness of the strobe system. However, a light loss occurs due to the concentric cylindrical surfaces of the annuluses of the Fresnel lens, axes of which being the optical axis, and hence it is difficult to obtain a large guide number. If a bi-convex lens which has no light loss is used, it is possible to obtain a large guide number. However, the bi-convex lens has a large thickness at the center portion thereof, thus resulting in an increase in volume. In addition, it is difficult to obtain the necessary thickness at the peripheral portion. Thus, the bi-convex lens makes it difficult to miniaturize the strobe device.